Time-dependent metabolic effects of portion-control plate interventions in adults with chronic diseases: a systematic review and meta-analysis

BACKGROUND: Dietary modification is central to chronic disease management, but conventional education-based approaches often require sustained self-regulation, which is challenging for populations with limited health literacy. Portion-control plates are an environmentally friendly tool that uses visual segmentation to guide portion selection. However, quantitative evidence on their metabolic benefits and whether these effects persist remains limited. AIM: This systematic review and meta-analysis aimed to evaluate the metabolic effects of portion-control plate interventions in adults with chronic diseases and to examine whether these effects vary across follow-up durations. METHODS: PubMed, Web of Science, Scopus, Embase, Cochrane library, CKNI, VIP, Wanfang were searched from January 1999 to July 2025. Data were pooled to calculate mean differences and 95% confidence intervals using a random or fixed effect model. To assess temporal dynamics, analyses were stratified by follow-up duration (≤ 3 months, 3-6 months, and 6-12 months). RESULTS: Fourteen RCTs involving 1,762 participants were included. Body weight showed early reduction at 3 months (MD = -3.68 kg, 95% CI -7.78 to -0.42 ), attenuating by 6 months (MD = -1.77 kg, 95% CI - 4.46 to 0.92). Hemoglobin A1c remained relatively stable across time points (-1.08%, -0.72%, and -1.10% at 3, 6, and 12 months; overall MD = -0.82%). Fasting glucose improved progressively from 6 to 12 months (P = 0.02 for subgroup difference). Low-density lipoprotein reductions were sustained at 6 and 12 months, while diastolic blood pressure improved only at 12 months (MD = -2.72 mmHg). Evidence certainty was highest for 12-month HbA1c and lipid outcomes. CONCLUSION: Portion-control plate interventions produce modest metabolic improvements with distinct time-dependent patterns, including early weight reduction, sustained glycaemic and lipid benefits, and delayed vascular effects. As a low-burden environmental strategy that can be easily delivered by public health practitioners and primary care providers, visually guided portion control may represent a scalable dietary intervention for chronic disease management. TRIAL REGISTRATION: The review was prospectively registered with the International Prospective Register of Systematic Reviews (PROSPERO; registration number CRD420251061435).